Wastewater treatment includes collection of wastewater from points where the wastewater is generated to treatment facilities where the wastewater is treated for reuse or discharge to the environment. Collections systems vary in design, based on the distribution of wastewater generation points and the general type of wastewater produced. Municipal wastewater treatment systems are examples of treatment systems where a particular treatment facility may receive wastewater, or sewage, from numerous points of generation that are distributed over sometimes very large geographic areas.
In the process of collecting municipal sewage, for example, collections systems include extensive arrays of piping and pumping stations. Thus, there may be miles of piping and tens to hundreds of pumping stations involved in one system. Moreover, municipal sewage, for example, comprises contaminants that support the generation and emission of various objectionable, noxious, and even dangerous and damaging gases. For example, the constituents of municipal wastewater include matter and organisms that support the evolution of sulfides in the wastewater. As a result, hydrogen sulfide gas may be emitted from the wastewater. Such emission of hydrogen sulfide gas within the collection system and treatment facilities the system serves can be quite damaging to this infrastructure, resulting in corrosion and failures of components in the system. Further, inevitable release of hydrogen sulfide gas to the environment creates an objectionable odor that is undesirable to those living and working near the system. Indeed, at sufficiently high concentrations, hydrogen sulfide gas can be injurious the humans and animals even to a point of causing deaths.
There have been various approaches to eliminating or reducing the emission and release of hydrogen sulfide gas from wastewater. Generally, extant approaches employ various configurations of control systems to control the injection of sulfide reducing or inhibiting chemicals into the wastewater. These typically involve sensing downstream hydrogen sulfide emission, and feeding back that information in a closed loop control system deployed at an upstream injection site. Such closed loop control systems thus attempt to form an error signal representing the difference in the desired downstream emission level and the measured downstream emission level by computing and injection an amount of chemical reactant apparently necessary to drive the error signal to zero. Such systems can be expensive due to remote emission detection and communication. Moreover, typical distances between chemical injection sites and measured emission sites on the collection network combined with varying flow conditions that impact residence time often create stability problems for such systems.
The influx of water from precipitation into the wastewater being treated for emission control can likewise have an effect on any approach to address the downstream emissions problem. Indeed, any entry of surface water or subsurface water into the collection system can cause problems. Extant approaches to addressing this problem have included remote and distributed monitoring of precipitation in efforts to account for the impact of water influx into the wastewater collection system. Many of these approaches suffer the same kinds of difficulties relative to stability as those described in cases of remote emissions sensing.
Further sensors and communications systems made necessary for many such approaches to the problem result in systems that are costly both to implement and to maintain.
Need exists for other approaches for downstream gaseous emission reduction or elimination in wastewater collection systems. Other approaches that tend to support stable and inexpensive operation are needed.